1. Field of the Invention
The present invention relates to a circuit for compensating for, corresponding to a change in temperature, the output of a sensor containing a resistor having a variable resistance value depending on the physical quantity of an object to be measured.
2. Description of the Related Art
A sensor containing a resistor having a variable resistance value depending on the physical quantity of an object to be measured is very popular. For example, with this type of pressure sensor, the resistance value of a resistor in the sensor changes with pressure, and the output current or output voltage of the sensor changes with the resistance value of the resistor. Therefore, a change in pressure can be measured by detecting a change in electric current or voltage. However, the amount of a change in a resistance value corresponding to a change in pressure normally depends on temperatures. Also, resistance value of a resistor itself and a characteristics of an amplification provided in a sensor depend on temperatures. Therefore, the output of a sensor has thermal characteristics and the temperature characteristics vary for each sensor. As a result, a temperature compensation circuit for compensating for the characteristics has been provided according to the conventional technology.
The temperature compensation circuit contains, for example, a resistor whose resistance value depends on temperatures, and the temperature dependency of the sensor can be compensated for by applying to the sensor an electric current or voltage generated based on the electric current flowing through the resistor. The Applicant of the present invention previously applied for a patent (Tokukaihei 7-20162) on the sensor output compensation circuit with the above described configuration.
However, in the conventional sensor output compensation circuit including the configuration according to the above described patent application (Tokukaihei 7-20162), it is necessary to perform a trimming process on a resistor provided in the compensation circuit such that the physical quantity of an object to be measured and the sensor output value can be equal to predetermined values. The trimming process is performed by detecting the output from a sensor a plurality of times with the measurement environment changed (for example, pressure and temperature for a pressure sensor), and trimming the resistor using a laser beam by referring to the detection result. Therefore, trimming devices have normally been very large and expensive.